The present invention relates generally to a hermetic scroll-type compressor and, more particularly, to such a compressor having an axial compliance mechanism, wherein an axial force acts on an orbiting scroll member to bias it toward a fixed scroll member for proper sealing therebetween during compressor operation. More specifically, the present invention pertains to such an axial compliance mechanism in which respective regions of discharge and suction pressure act on the bottom surface of the orbiting scroll member, and sealing is provided between the respective pressure regions.
A typical scroll compressor comprises two facing scroll members, each having an involute wrap, wherein the respective wraps interfit to define a plurality of closed pockets. When one of the scroll members is orbited relative to the other, the pockets travel between a radially outer suction port and a radially inner discharge port to convey and compress the refrigerant fluid.
It is generally believed that the scroll-type compressor could potentially offer quiet, efficient, and low-maintenance operation in a variety of refrigeration system applications. However, several design problems persist that have prevented the scroll compressor from achieving wide market acceptance and commercial success. For instance, during compressor operation, the pressure of compressed refrigerant fluid at the interface between the scroll members tends to force the scroll members axially apart. Axial separation of the scroll members causes the closed pockets to leak at the interface between the wrap tips of one scroll member and the face surface of the opposite scroll member. Such leakage causes reduced compressor operating efficiency and, in extreme cases, can result in an inability of the compressor to operate.
In most scroll compressors, the fixed and orbiting scroll members are precisely machined so that the height of the respective involute wrap elements are substantially equal, thereby insuring proper sealing between the wrap tips and face surfaces. In such a compressor, it is often the practice to manufacture and assemble the compressor so that the orbiting scroll member is initially in sealing contact with the fixed scroll member. This may be accomplished by holding tight dimensional tolerances on various machined compressor components, e.g., fixed and orbiting scroll members, frame member, crankshaft, orbiting scroll member drive mechanism. A primary disadvantage of this approach is the difficulty and expense associated with trying to achieve close stack-up tolerances with a plurality of associated parts.
Alternatively, the scroll members may be preloaded toward each other to facilitate sealing contact, i.e., with a spring mechanism or resilient seal means. When the scroll members are initially in sealing contact with one another, high frictional forces between the scroll members cause difficulty during compressor start-up. Furthermore, an expensive thrust bearing may be required to bear the separating force between the fixed and orbiting scroll members.
In an effort to avoid the manufacturing and operational problems associated with scroll compressors wherein the fixed and orbiting scroll members initially sealingly contact one another, axial compliance mechanisms have been developed in which the orbiting scroll member is initially spaced from the fixed scroll member and then moves axially toward the fixed scroll member to sealingly engage after compressor start-up. In U.S. Pat. No. 4,645,437, issued to Sakashita et al., an annular chamber containing gaseous refrigerant at discharge pressure is exposed to the bottom surface of the orbiting scroll member to cause it to shift slightly upwardly. A pair of radially inner and outer seal rings move axially upwardly along respective tapered chamber walls so as to remain in sealing contact with the bottom surface of the orbiting scroll member. Accordingly, the annular channel is initially sealed and remains sealed during axial movement of the orbiting scroll compressor.
One disadvantage of all the aforementioned axial compliance mechanisms is the fact that the compressor experiences loading very quickly upon start-up, due to either initially sealed compression pockets or an axial compliance mechanism that is quickly actuated by compressed gaseous refrigerant. If loading occurs prior to the crankshaft bearings being lubricated with oil, premature failure of the bearings may result. Also, many prior art scroll compressors, wherein the orbiting scroll member is permitted to move axially, experience excessive oil rates, i.e., the percentage of lubricating oil entrained in the refrigerant fluid. This is caused in part by the fact that in the differential pressure oil pump system commonly used in the prior art scroll compressors, axial displacement of the orbiting scroll member provides less restriction for flow of lubricating oil from discharge pressure regions to suction pressure regions. Furthermore, despite prior art attempts to seal between respective regions of gaseous refrigerant at discharge and suction pressures, sealing of gaseous refrigerant remains a difficult task and results in a "dry" seal that is less effective at higher compressor operating speeds.
The present invention is directed to overcoming the aforementioned problems associated with scroll compressor axial compliance mechanisms, wherein it is desired to provide a reliable seal between respective regions of discharge and suction pressure on the bottom surface of the orbiting scroll member, despite axial movement of the orbiting scroll member toward the fixed scroll member.